Treatment of fibrous glass



March 26, 1968 R. G. ADAMS 3,375,155

TREATMENT OF FIBROUS GLASS Filed Aug. l5, 1966 2 Sheets-Sheet l l f U fu Y l N f l Q '1- l `V f o u. l 9 K f f e l v/ h.\/ D )f n INVENTOR.@www 6. Hams March z5, 196s vR. G. ADAMS 3,375,155

TREATMENT voF FIBRoUs GLASS Filed Aug. 15, 1966 2 Sheets-Sheet 5&5 (I) Ii as l o @s 5 5 5 5 fum/y w//rgy MAQ/@dug QA//fwgg R INVENTOR.,Pfaff/#Q0 G. ADQ/15 Anw/VC-YS United States Patent 3,375,155 TREATMENTOF FIBROUS GLASS. Richard G. Adams, Upper Montclair, NJ., assignor to J.P. Stevens & Co., Inc., New York, N.Y., a corporation of DelawareContinuation-impart of application Ser. No. 284,220,

May 29, 1963. This application Aug. 15, 1966, Ser.

10 Claims. (Cl. 161-93) ABSTRACT OF THE DISCLOSURE A process .forheat-cleaning fibrous glass, such as textiles, in such a manner as. toinhibit strength loss by following the steps of treating the glass withan oxygen yielding salt of potassium, sodium, cesium and rubidium,drying the treated glass (if not alreadydry), and then heating thefibrous glass at a temperature of between about'` 0 600 F. and 1250"7 F.until substantially all of the sizing has been removed, i.e, until theignition loss is about 0.1% or less. Optionally, further heat treatmentis applied to increase tensile strength.

Also, the fibrous glass which has been desized accord- 5 ing to theforegoing procedure, said glass being characterized by a tensilestrength of at least 70% of that of the untreated greige fabric, andhavingl an excellent white color.

This invention relates to the production of heat-cleaned fiber glassVand is a continuation-impart of my earlier application of the same titleSer. No. 284,220, filed May 29, 1963, now abandoned. The inventionrelates more particularly to a method for heatcleaning fiber glassfabri'c in a manner which gives` a. good white colorl andI minimizesstrength loss.

To protect glass fibers a coating of` sizing ifsV applied, to, thesurfaces thereof as soon after the spinning of the fibers as ispractical. The sized fibers` are then usually woven or fabricated intothe fabric form. Prior toy dyeing and finishing, the sizing mustl beremoved' from the glassl fibers The generally accepted method ofremovingsizing in the fiber glass art involves the use of treatment at elevatedtemperatures. i

In general, heating the fiber glass to high temperatures results in theremoval of the sizing material; and' any` other thermally sensitivecompounds, such as lubricating oils, present on the fibers, Adistressing1 problem in the p iber glass heat-cleaning arti istheAsteady degradation, o f' the strength o f'the fabric which obtainsduringsuch'cleaning, especially when such heating is carriedon for atime` sufficient to` achieve an acceptable white color. The patent 55literature in' thisv area is evidence of'thecontinuing search for newand better methods; off heat-cleaning which will' notr sufferY from thedisadvantage of s'trengs'thfdeg/radation.,

U.S. Patent No. 2,633,428 issued to C; Klug on Mar. 31', 1953, describesa process commonly referred` to as 60 Coronizing. The Coronizinglprocess involves exposing the liberA 'glass fabricY to air in a furnacemaintained atelevated temperature-s, for example, between lj100 F. and y1400 F. Cleaning is accomplished by combustion on the `withheat-cleaning. n t y It is afurther objectfof theinvention to prox/idealproc- .f

,Period 3,375,155 Patented Mar. 26, 1968,

icc

the tensile strength ofthe processed fabric.

U.S. Patent No. 2,970,934 issued to M. R. May on Feb. 7, 1 961,describes a method which is reported to be superior? to Coronizinginrespect of the tensile strength of the cleaned fabric. lThe May=lpatent discloses ar process inl which the fabric, is introduced into afurnace, much in the.. same manner as. Coronizing. However, the amountof oxygenA suppliedv to the furnace is limited to an: amount' sufficientonly to support combustion of the sizeA with a4 yellow,carbon-containing, wide, lazy llame, as distinguished from a blue llame(see column 2, lines 61-631).

Both the Coronizing process andthe process described in the above patentissued to M. R. May are discussed in US., Patent No. 3,012,845 issued toE. L. Lotz on Dec. 12, 1961. According to Lotz, the Coronized fabric hasa tensile strength which is only about 30% to 60% of that of the greige.goods (see Lotz, column 2, beginning at line 20). f

According to Lotz,A although the process described" by' May in the abovepatent provides an improvement in tensile strength, the fabric does notexhibit a white color.V

U.S. Patent No. 2,674,549' issued to-E. H. Balz de` scribes a processwherein the sized `liber glass fabric vis soakedl in a solution ofalkali chlorate and then placed', while wet, into a furnace at verymoderate times (30seconds to 1v1/2 minutes) and temperatures (650-750"F.)`.v

Balz showed that the presence vof the chlorate oxidizing salt assistedin the removal of the sizing. However, the

heat-cleaning step though short, was not always successful in givingA awhite product and frequently a time-con- -sumfng after-treatmentA ofbleach was necessary to achieve acceptable White color.l There is;evidence as; well that modest time-temperature heating; conditions; inthe pres-l ence of a chlorate solution result inpexcessive loss in fab--ric strength.

Accordingly, it isan object of this invention to provide a process forheat-cleaning fiber glass which minimizes strength, loss.

It; iS 2l. yfurther object o f they presentinvention tol pro:- v

Vide a process for heat-cleaning fiber glass to an excellent whitecolor.

,Ity isl another object of thepresent invention to-provide a process`forininimizing the time required to obtain anl acceptable 'whitelheat-cleaned fiberk glass fabric,A while. simultaneously minimizingthe-'strengthA loss associated ess for heat-cleaning fiber glasswhichis, applicable; to a wide range of 'temperaturcsandi timeconditions.

yIt is another; object lof the-presentiinvention'toprovide a cleanedwhite ber glass fabric-of relativelyI high ten,- sile strength. v

Briefly stated, one embodiment of; the presenti invention isa method, ofheatfcleaning tibrousglas-sto remove f the"v sizing materials comprisingthe steps of treatingtheglass withl a substance comprisingacation.selected from the group consisting of sodium, potassium, cesium andrubidiunnand ananion decomposablevby. heat to provide oxygen, andheating theV glass, While dry, jto atemperature in the approximate range0f 600 F. to` l250 F. for a v of time atleast suicient to removesubstantially. y

allof the sizingmate'rial.

It has been discovered that when a fibrous glass fabric is subjected tothe above treatment, the resulting fabric is not only sufficiently whiteto obviate the necessity of any bleaching treatment, but the fabric isunu-sually strong as compared with ordinary heat-cleaned fabrics.

Thus, by following the teachings of the present invention there may beobtained, for the first time, a heatcleaned fibrous glass fabric whichhas an excellent White color and which has a tensile strength, Whenfinished, that is no less than 70% of that of the greige fabric.

It has been found that, unlike ordinary heat-cleaned fabrics whereintensile strength steadily decreases with increased` heating time, thefibrous glass materials treated according to the p-resent inventionactually exhibit a pronounced slowing down in strength degradation, evento the point of frequently exhibiting an increase in strength withcontinued heating. This minimizing of the strength loss which normallyattends the heat-cleaning process is characteristic of the presentinvention and is wholly unexpected. The actual degree to which thestrength loss is minimized, and the extent of any actual strengthincrease is dependent upon a number of factors,

particularly the selection of cation, the .temperatures used, and thetime of heating.

By treating a fibrous glass gabric according to the process of thepresent invention it is possible to heatclean a fabric to an acceptablewhite color in far shorter time than would be required in the absence ofsuch a process. Moreover, the resultant fabric will be strong orstronger than the untreated fabric heated at the same temperature for anequivalent time, and it will be mucllf stronger than an untreated fabricwhich has been heated for a sufficient time to produce equivalentwhiteness.

According to the process of the present invention, the time of heatingof the fibrous glass, irrespective of the temperature chosen, isat leastthat required to remove substantially all of the sizing materials. Thetime required to accomplish this will naturally decrease with increasingtemperature. Moreover, the time required is also dependent upon theweight of the fabric chosen (longer time for heavier fabrics) and uponthe specific nature and amount of sizing on the glass fiber. Obviously,no precise range of time conditions can be set for a given temperature;the precise time for each given situation must necessarily be arrived atempirically, a procedure that is well within the skill of those versedin the art, once the criteria for whiteness, furnace temperature, andthe like, are considered.

In any even-t, the time is at least that required to removesubstantially all of the sizing materials, and this condition is readilyascertained by means of an ignition loss test. As defined herein,substantially all of the sizing has been removed when the ignition lossis about 0.1% (by weight) or less.

An even more convenient means of measuring sizing removal is throughmeasurement of the whiteness of the fabric; that is, an acceptable whiteheat-cleaned material is -`substantially free-of sizing. There arevarious means available to measure whiteness and one of these is thephotoelectric refiection meter. Measurements taken with such aninstrument are found to correlate relatively well with ignition loss andhence provide a quick check on the state of cleanliness of the fabric.

The foregoing attributes of the present invention are more readilyunderstood by vreference to the figures, in which:

FIG. l illustrates the time-strength relationship at differenttemperatures of a fibrous glass fabric treated according to oneembodiment of the present invention as well as the correspondingtime-strength relationship of an untreated control fabric. .A

FIG. 2 describes the time-strength relationship atdifferentternperatu-res of al fibrous glass fabric treated according toanother embodiment of the present invention, as -well'as a correspondingtime-strength relationship of a fabric treated according to one of theknown heatcleaning processes.

Referring first to FIG. l, there is shown in solid lines asemi-logarithmic Iplot of time against tensile (or breaking) strength(in pounds per inch width) of various specimens of glass fabric thathave been treated by a solution of potassium nitrate, dried, and thenheated -at given temperatures. In this instance potassium has beenselected as representative of the cations useful in treating the fibrousglass according to the invention, and nitrate has been selected as asuitable anion decomposable Iby heat to form oxygen. Each curve, of FIG.1, for a given temperature has been obtained by heating several samplesof potassium nitrate-treated E glass fabric for various times, testingeach such sample after finishing for tensile strength, plotting theresultant time-strength points on the t graph and then drawing a smoothcurve through the data points. The -point at zero time represents thestrength of a greige fabric. The conditions used as well as the testingmethods are discussed more fully hereinafter with reference to Examples1 and 2.

As shown in FIG. 1, the time-strength relationship was obtained for fourwidely different temperatures, i.e. 650, 700, 900 and 1000 F. It will benoted that there are certain common characteristics shared by all f ourcurves:

(l) All curves show a characteristic decreasing strength shortly afterheating is begun. A small initial strength rise at the lower temperature(650-700 F.) is quickly dissipated. The strengths all decrease for agiven period of time and then as heating is continued, there is anunexpected slowing down in the strength lossfollowed by a noticeableincrease in strength to a maximum value, and, eventually a tapering offof the strength at a value that is not below the lowest initial value.

(2) The times at which the various samples exhibit the characteristicsdescribed in (l) above, and more particularly, the point at which thestrength decrease inverts to a strength increase differ from one to theother depending on the temperature of heating.

Quite noticeably, the higher the temperature, the earlier the effectsare exhibited. Thus, at 1000 F. the strength loss terminated at about 6seconds, whereas at 700 F. the correspondingV point did not occur untilabout 6 minutes of heating.

The maximum strength values shown lby each sample (corresponding, forexample, to the point A on the 1000 curve) follow `the same pattern.

(3) The maximum strengths, such as that represented by the point A onthe 1000 F. curve, become lower as the heating temperature is increased.Thus, at 1000 F. the maximum strength valve is about 175 pounds/in.width, whereas at 700 F. the maximum value is about 203 pounds/in.width. In each case, however, the maximum strength value is well aboveof the original greigestrength-a remarkably high strength for aheatcleaned glass ber. Indeed, at the lower temperatures, as for example650 F., at no time does the strength fall below abou-t of the originalgreige strength and actually reaches a maximum value (after about 5hours of heating) of about of the greige strength.

An interesting and significant phenomenon occurs as a fibrous glassfabric is heated for various times at given temperatures as depicted inFIG. 1. It has been found that irrespective of the temperature ofheating, the point at which the fabric has been heat-cleanedsufficiently to remove substantially all of the sizing thereoncorresponds generally to the point of strength inversion. For example,the specimen heated at 900 F.. as shown in FIG. 1 was cleanedsubstantially free of sizing after about 14 minutes, i.e. at a point intime corresponding well with the inflection point B in the strengthcurve.

Therefore, according to the present discovery, in order to obtain a goodwhite glass fabric as well as one having a minimized strength loss, itwould be necessary to heat 4tested identically to those preparedaccording to the invention except, of course, they were not treated withthe cation-oxidizing agent of the invention.

By comparing the strength rvaluesfor specimens heated at the sametemperature it is, readily apparent that the process of the inventionhas a pronounced beneficial ef'- fect upon the strength of the fabric.The control samples show the expected deleterious strength loss patternwhichl is associated with ordinary heat-cleaned glass fibers. It isnoted that the curves for the control samples roughly follow those ofthe KNO3 treated fabrics during the initial heating period, and thenalthough the strength lossof the treated samples isinhibited asdescribed' above,

the control samples continue to exhibit a steady strength loss.

Equally revealing is the fact that the control `samples did not becomesubstantially free of sizing until heated for a far longer time than wasrequired for the treated samples. For example, at 900' F. it tookv over5y minutes (corresponding to point D of FIG. l) before the controlsample was cleaned to an excellent whitey color. The correspondingpointv for the treatedv sample at 900 F. took less than 12 seconds(point B of FIG. 1).'Signilcantly, the strength of the control sample atthe time it became cleaned to an excellent white was about 90. lbs/in.width as compared with about 159 lbs./in. width for the treated sample.Moreover, continued heating of the treated. sample; actually increasedthe strength of the sample to a maximum value of 186 lbs/in. width(point C of FIG.. 1) v while simultaneouslyimproving evenfurtherthe-whitenessofthe fabric. By wayof contrast, continued heatingof the control fabric at 900 F. caused a continuing` slow declineinstrength without any substantial improvement in fabric color. Y g

In FIG. 2 the solid lines represent the strength-.time curve at thegiven moderate temperatures for a fibrous glass fabric which has beentreated with potassium chlorate according to the process of the presentinvention. With the exception of the use of the chlorate anion as thesource of. oxygen rather than nitrate, the process. used forFIG. 2 wasotherwise identical to that used for FIG. l.

FIG.v 2 shows that a treatment with potassium chlorate gives slightlydifferent time-strength behavior than treat-.. l

mentwith potassium nitrate. The former does not exhibit any substantialincrease in strength as heating is con tinued. Nonetheless, the.precipitous loss inv strength that is associated with ordinaryyheat-cleaning, as represented by the control fabric curves of FIG. 1, islargely abated'.

A comparison of the strengthvalues at 700 F., for ex'- ampl'e, of theKClO-treated material (FIG. 2) and the untreated control (FIG. 1')readily points up the fact thata considerable relative improvement instrength has a superior performance compared tof the chlorate anion maybe caused by the decomposition ofthe chlorate to the chloride form. Thechloride salt is relatively infusible at the furnace temperaturesencountered and thereforev tends to inhibit good surface contact betweenthe cation and the glass liber. On the other hand, the: nitrate saltsremain in the fused state throughout the heat-cleaning" process andtherefore ypermit good contact of the active materials with the libersurface.

Referring again to FIG. 2, there is shown in dotted lines thestrength-time relationship at given temperatures for a glass fabricwhich has been treated'with a solution of potassium chlorate andintroduced into the heating-furnace while still wet. This procedure,when confined to the time limits of30 seconds to 1%' minutes, is inaccordance with the teachings of the aforementioned Bal-z Patent No.2,674,549. This procedure improved the rate of cleaning asl comparedwith the control fabric; however,` there was no noticeable. abatement inther strength loss.`

Indeed, the strengths were considerably below those of the KC103-embodiment of the process according to the present invention (whereinthe treated glass fabric is dry rather than Wet when placed into thefurnace), as may be seen by a comparison of the, dotted lines in FIG." 2

with the corresponding solid linesat the same temperatures.

The modest temperature-time cycle of the wet procedure is notvparticularly successful in yielding acceptable white materials, itIhaving been. found generally necessary either to extend the heatingtimeor to include a bleach-- ing step. Moreover, the relatively reducedstrength of* fibrous glassv heat-cleaned by the so-called wet procedurehas been found to not improve substantially even when the heating iscontinued for extendedlengths of time, ile. for several hours.

It is concluded, therefore, that the full benefits of the presentinvention are not achieved at least insofar as the chlorate salts areconcerned, unless the treated fabric is. substantially dry whenintroduced into the heating area.

Having thus discussed the main attributes and benefits of the presentinvention, other Iattributesl and benefits will become apparent uponconsiderating` the following examples. Example 1 A control sample wasprepared and tested in the man:

ner set forth hereinafter for purposes of comparison with the results ofsubsequent examples utilizing the pre-treatment of the invention.

For these purposes a fibrous glass fabricwas chosen (style 473) havingthe following characteristics: 4.4 oz./

1 sq, yd., warp and fill ECDE 150y 12/0 lZ ber glass yarn.

' Specimens of the greige, fabric,` without pre-treatment, .wereheat-cleaned in an, air circulating oven at tempera.-

tures of 650 F., 700F., 900 F. and 1000 F for vari-A ous. times, rangingAfrom a few seconds to several hours.`

t The temperatures and times-were chosen to give a. Wide range of datarepresentative of the behavior of the fabric.

been achieved -by the- KClOaytreatment. This is all the control fabricwas reached only after about 36|mnutes of heating and at a strengthvalue of l22lbs./in. width. Thus the control took about four times aslong to get clean, and, as cleaned, was about 20% less strong.

. FIGS. l and 2 show that the relative' improvement of the invention mayvary depending upon theparticular,

oxidizing agent used. The fact that the nitrate anion gives Thereaftereach specimen was coated with anish of an ethylacrylate polymer latexmodified by an epoxidizedl vegetable oil, and then tested for tensile.strengthk and cleanliness. Tensile testing, reported in lbs/in. width,was done according to Owens Corning Fiberglas Corp. Standard TestMethods for Fiberglas Decorative Fabrics, Technical Report No. 175, TestNo. DF-509; also ASTM D579-49.

The cleanliness was determined by measuring-the whiteness: of thefabricwith a photoelectrick reflection meter,

and. more particularly a Photovolt model 6.10` equipped witha. greentristimulus, filter.` This. commonly used in,

strument is designed to measure they diffuse reflection of'` surfaces,and particularly luminous apparent reiiectance Y as an indication` ofdegree of whiteness, and is described more fully in Bulletin No. 605,vPhotovolt Corp., 9,5 Madison Avenue, New York, lN.Y., and in' Color inBusineseg.:

8 ple such a treatment yielded an excellent'white fabric with aphotoelectric reading of 76, thus indicating that acceptableheat-cleaned fabrics should not have readings less than roughly 90% ofsuch a standard.

The tensile strength (at break) and the photoelectric' data for thecontrol fabric are given in Table I below.

TABLE 1.-(CONT ROL) Y 650 F. 700 F. 900 F.' 1,000 F.

Time Strength, White- Time Strength, White- Thne Strength, White- TimeStrength, WhitelbsJin. w. I ness lbs/in. w. ness lbs/in. W. ness lbs/in.W. ness 227 227 227 227 240 62 220 58 196 49 148 5.0 229 59 195 56 15149 122 61 198 55 181 54 132 58 112 65 170 54 169 54 128 64 108 68 161 45163 50 108 68 99 70 134 49 155 53 110 71 95 71 121 55 140 62 94 72 87 73104 60 122 70 91 74 92 73 96 71 1.25 HIS.- 104 75 85 75 85 74 98 76 2.5-96 75 72 75 89 74 89 76 93 75 75 76 81 75 92 77 8 Hrs 92 75 79 76 76 76It was found that photoelectric readings in the range Example 2 of about70 to 75 corresponded well with average fabrics that had beenheat-cleaned to the point that ignition loss was 0.1% or less. Hence,for ease of experimentation, photoelectric tests were used to give quickdeterminations ofthe removal of substantially all the sizing. A readingof about 70 or more indicated that the fabric was clean. A reading ofabout 70 was found to correspond to an ignition loss of about 0.1% andthe fabric color was a fair White. At readings of about 73-74 the colorimproved to a good white, and at 75 and above the color was an excellentwhite.

It must be appreciated that the photoelectric meter reading on fabricscan be influenced by changes in the texture of the fabric or even in thedesign of the meter itself. For this reason itis sometimes helpful,especially when relatively rough or heavy fabrics are being examined, tocompare the readings of the subject specimen Specimens of the same style473 greige fabric as used for the control were treated with a 3% aqueoussolution of potassium nitrate in a textile padder, and the excess liquidremoved. The fabric wet pick up was about 30% or about 1% on the drybasis. The fabric was then dried.

The dried-fabric specimens were then introduced into an air circulatingoven at different temperatures ranging from 650 F. to l000 F. land forVarious times, ranging from av few seconds to several hours.

Following the heat treatment each sample was immersed in a water bath,then in a 3% acetic acid solution, and then finally in a running-Waterrinse.

After drying, the specimens were finished with the modified acrylicfinish referred to in Example 1- and then tested for tensile strength(at break) and whiteness (by the photoelectric method). The resultsobtained are given in Table 2.

. TABLE 2.- (KNO3) 650 F. 700 F. 900 F. 1,000 F.

Time Strength, White- Time Strength, White- Time Strength, White- TimeStrength, Whitelbs/in. w. ness lbs/1n. w. ness lbs/in. w. ness lbs/in.w. ness 227 227 227 Gl'elge- 227 253 37 253 33 192 52 5 Sec 141 77 24236 232 38 159 76 10 Se!! 140 78 238 39 214 47 167 76 14 Sec 172 77 A 21446 201 55 186 79 20 Sec 173 77 191 55 191 67 184 77 30 Sec 177 79 195 59175 72 181 77 42 Sec 158 77 188 74 205 77 163 77 1 Mln 158 78 186 77 199`78 162 77 1.5 Min. 153 78 195 78 198 78 168 78 2 Min- 152 79 204 77 19678 163 78 3 Min. 143 79 208 77 186 79 166 79 4.5 Mi 155 78 192 78 8HI'S. 186 79 172 78 6.5 Mi 156 78 158 78 10 Min..- 145 78 with those ofcomparable fabrics of known excellent Example 3 whiteness. The unheatedgreige fabric is suitable for this purpose. In the instant example, thegreige fabric had a photoelectrioreading lof 8l. This indicates that anacceptable thermally de-sized fabric should not have a photoelectricreading of less than about 85% of that of the greige fabric.

Another excellent white standard is that achieved by heat-cleaning anuntreated sample for a relatively long time, say for 4 minutes at 1000Fjln the present exam- Example 4 The process of Example 2 wasreepated'exceptthata 3% solution of cesium nitrate was used insteadV ofpotas-" sium nitrate. The results are given below in Table 4. 1

TABLE 3.-.(RbNOa) 700 F. 900 F. 1,000 F.

Time Strength, whiteness Time Strength whiteness Time Strength whitenesslbs/n. w. lbs./ inw. lbs/1n. w.

TABLE 4.-(CsNO3) 700 F. 900 F. 1,1000" F.

Time Strength, whiteness Time Strength whiteness Time Strength whiteness1bs./in. w. lbs./ in.w. lbs/in. w.

227 Greige. 227 227 234. 29 193 77 181 77 233 40 182. 78 159 76 228 41168 78 205 77 192 66 196 79 229 77 188 6 9 216 78 '234 77 204 75 205 78224 77 203 78 189 78 232 76 197 78 f 213 77 227 77 184 77 217 78 223 77166 77 215 78 217,' 79 150 76 196 78 200 79 140 77 189 79 175 79 Y 17179 153 79 It is readily apparent from the data tabulated in Tables 3 and4 that the cesi-um and rubidium cation give exceptionally good resultswhen used in accordance with the invention. In each instance, andirrespective of the temperature of heating, there are obtainedexceptionally good strength characteristics. For example, in the case'Aof cesium nitrate at 1000 F., there is obtained after only 30 seconds ofheating an exceptionally clean white fabric that has a tensile strengthas good as the greige fabric.y In the case of rubidium nitrate, allspecimens could be cleaned free of sizing within a few seconds to a fewminutes while maintaining a strength of between about 80% and 90% of thegreige fabric.

These data (Tables 3 and 4) also show the inversion in strength losswith subsequent strength increase that characterized the behavior ofpotassium nitrate as set forth in FIG. l. Moreover, the strength lossinversion was again found to correspond well with the point at which thefabric became substantially free of sizing as indicated by the whitenessdata. The results also suggest, that if processing time is important andstrength is not an overriding consideration, the process may be stoppedwhen substantially all the sizing has been removed.v However, if bothcleanliness and strength are of paramount importance, then heating maybe continued for a period of time to take advantage of the increasingstrength characteristics.

Although the data of Tables 3 and 4 indicate that the rubidium andcesium cations .give a performanceslightly better than potassium, thelatter is preferred because it is comparatively much'less'expensive.

Example 5 The same procedure was used as described.v above Example 2except that'a 3% aqueous solution of sodium dent that the sodium cationshows considerably better.

strength properties at the lower temperature levels than it does at thehigher temperature levels. At 650 F., for instance,"the sodium treatedsample was substantially clean after 18 minutes of heating and had astrength of 220 lbs/in. width. By way of comparison, the potassiumtreated sample (Table 2) was also clean after 18 minutes, but had astrength of 1&8 lbs/in. width.

On the other hand, at 1000 F. the cleaned sodiumtreated specimen didnot-succeed in reducing the strength loss quite as successfully as didthe corresponding potassium-treated specimen, even though it was muchstronger than the control. It is apparent, therefore, that the selectionof the best cation may depend uponrthe requisite operating temperature,

TABLE 5.-(NaNo3) 650 F. 700 F. 900 F. 1,000 F.

Time Strength, White- Time Strength, White- Time Strength, White- TimeStrength, White lbsJin. w. ness lbs/in. w. ness lbs/in. w. ness lbs/in.w. ness Example 6 Example 8 Example 2 was repeated except that a 3%solution of potassium ehlorate was used instead of the potassiumnitrate. The results are given in Table 6.

As referred to before in connection with FIG. 2, the results obtainedwhen using the chlorate anion are slightly different than those obtainedby using a nitrate anion, and the separate data points are morescattered even though they indicate a marked and significant improvementin strength over the control. This behavior of the chlorate is believedto be associated with the infusibility of the chloride to which it isreadily decomposed. Because of this, the nitrate anion is preferred overthe chlorate, though both `are considered satisfactory, as is any aniondecomposable by heat -to form oxygen, e.g. bromate, iodate, persulphate,and the like.

A casernent type fiber glass fabric style 429 (4.4 oz./ sq. yd. warp andlill ECDE 150 1/0 lZ fiber glass yarn) was treated with solutions,respectively, potassium nitrate, rubidium nitrate and cesium nitrate.

Specimens of each of these treated fabrics were dried at moderatetemperatures and then heated at 1000 F. for various lengths of time aswas a control specimen. The heat treated specimens were then coated witha Vfinish based on an ethylacrylate polymeric latex of the type 0 1962,o.C.F. Test #DF511.

The samples were cleaned to an excellent white color TABLE 6.-(KC103)650 F, 700 F. 900 F. 1,000 F.

Time Strength, White- Time Strength. White- Time Strength, White- TimeStrength, White- 1bs.lin. w. ness lbs/in. w. ness ibs/in. W. ness s/in.w. ness 227 227 Greige. 227 Greige- 227 268 31 231 32 15 See 227 33 5Sec 147 50 263 35 229 34 30 Sec 224 35 10 Sec 136 61 237 37 223 36 1 Min215 41 14 Sec 138 65 231 39 199 41 2 Min 190 62 20 Min- 144 68 219 42183 60 4 Mn 169 73 30 Min- 130 70 188 60 152 71 9 Min 179 76 42 Sec 15471 178 67 158 75 18 Min- 194 77 1 Min 139 73 166 70 149A 72 36 Min 17977 1.5 Min 147 73 173 73 1.25 H1s 154 76 1.25 Hrs 179 77 2 Min 146 74158 75 v2.5 Hrs- 149 76 2.5 Hrs 176 76 3 Min 153 74 153 75 5 Hrs-- 15976 5 Hrs 179 76 4.5 Min. 134 75 146 78 8 HrS-- 144 77 8 Hrs 179 77 6.5Min. 126 76 y 1o Mmm-. 131 76 Example 7 after about 10 seconds exposure,:and were noticeably Example 2 was repeated except that a 3% solution oflithium nitrate was'used in place of the potassium nitrate. Inv thiscase, the separate specimens of fabric showed whiter than the controlsample after the latter had been exposed for seconds, which was the timerequired to clean theVV control sample to an acceptable white color.

rapid and complete"strengthfailure at all temperatures. In eachinstance, as well, the Mullen Burst Strength was found to be well abovethat of the control, and even in excess of the original greige fabric.

Example 9 A speciment was given a pre-treatment, with a solution ofpotassium nitrate as described in Example 8, dried, and thenheat-cleaned at 1050 F., as was a control fabric. After 3 seconds thetreated fabric was clean and had a Mullen Burst Strength, ywhenfinished, of 386 p.s.i. The control was clean after 30 seconds and had aMullen Burst Strength of 270 p.s.i. The greige strength was 371 p.s.1.

Example 10 Casement style glass fabric style 429 (4.4 oz/sq. yd., warpand fill ECDE 150 1/0 lZ.) was treated with a 10% aqueous solution ofpotassium nitrate in a textile padder. A wet pick up of 30% resulted ina dry application of approximately 3% by weight of the salt.

The dried fabric was exposed in an air circulating oven for 1 hour at700 F. The heat treated fabric was then washed in water to removesoluble salts and was finished with acrylic latex finish to protect thefibers against selfabrasion.

The finished fabric had a Mullen Burst Strength of 547 p.s.i. incomparison with 354 p.s.i.,for the greige fabric. The treated fabric wasexceptionally clean and white.

Example 11 Style 429 Casement fabric as described in Example 10 wastreated with a 5% pot-assium nitrate aqueous solution in a textilepadder with approximately 30% wet pick up.

The dried fabric was passed continuously through a laboratory mufflefurnace (4 inches long in the direction of fabric travel) `at 1000 F. ata speed of 1% yards/ minute'. The fabric wasthen washed and finishedwith acrylic latex finish. The Mullen ABurst Strength ofthe finishedfabric was 406 p.s.i. and the fabric was exceptionally white.

In the various processes described above for treatment of the fiberglass in accordance with the present invention,

a fabric has been the end product. In those instances where fiber glassfabrics are to be treated in accordance with the present invention, onemethod of applying the salts disclosed herein is from an aqueoussolution. The aqueous bath which is used should contain a concentrationof salt in a range from about 1% to 10% by weight. In the conventionalpadding technique the weight pick up yof the fabric is about 30% liquidper unit weight of the dried cloth. Thus, when using va v10% solution,with a pick up of 30%, there would be approximately 3% salt by weightbased on the dried fabric.

In general, the salt pickup, on a dry basis, should be at least 0.3% byweight of the glass` fibers treated in accordance with the presentinvention. In other words, if potassium nitrate is'to be applied toglass fibers in fabric form, the potassium nitrate should be present onthe fiber glass to an extentequal toat least approximately 0.3% byweight based on the glass fibers to achieve` a notable improvement.Preferably, the salt pick up should be in the approximate range 1 to 5%by weight. Greater amounts may, however, be required to obtain uniformdistribution of the dried treatment on the surface of the filaments.

Following the impregnation of the fabric with the aqueous salt solution,the fabric isdried. This step avoids the deleterious effects upontensile strength that accompany wet introduction of the fabric.Moreover,it is to be appreciated that the introduction of largeamounts ofWaterinto the high temperature oven would make it very difficult tomaintain the desired temperature in the oven. The salts may also beapplied to the fabric from a hot melt, or may be distributed in granularform over the surface of the fabric and then be fused..-The manner-ofapplication is not material so long as the distributionv is relativelyuniform. Y

f The salts of the present invention may also be added to the starch oilsize which is commonly applied to fiber glass yarns in the first step oftheir manufacture. This is advantageous because the salts are thenpresent on both Warp and filling yarns without the necessity ofanyadditional treating operation.

In the processing of glass fiber fabrics according to the invention ithas been found highly advantageousy to follow the heat treatment with anacetic acid wash.

Thorough washing at this stage is required in order to v avoidembrittlement and weakening of the glass fibersa result that isapparently caused by self-abrasive damage by inorganic residues. Theseresidues also tend to stiffen the hand of the fabric and inhibit finishpick up. Ordinary washing with water frequently fails to remove all ofthese inorganic residues. Thorough water Washing is satisfactory, but isexpensive and time consuming. However, by interposing an acetic acidbath these problems are minimized. Apparently the inorganic residues areconverted to acetate salts that are much more soluble in water, with theresult that subsequent waterwashing removes considerably more residue.Moreover, even relatively poor washing of the acetic bath treated fabricdoes not degrade the fabric strength since the acetate salts arerelatively soft and non-abrasive. Wetting agents may also be added tothe acid bath or Wash water to assist in removal of the inorganicresidues.

For this purpose, an acetic acid wash bath of 1 to 10% is generallysatisfactory. A concentration of about 20 to of that of the alkali saltsolution is preferred. An excess of acetic, acid is not harmful providedthe Washed fabric is adequately dried.

In another embodiment of the invention, the salts can be applied to thewarp yarns only during the conventional warp sizing step. For treatmentin this manner, the salts of the present invention are added to a warpsizing as a component thereof, and the `fiber glass yarns are treated inthe usual manner. Thus, the salts of the invention arey present on thewarp yarns together wih the sizing material. The fabric is then wovenand during the cleaning step the salts exhibit the same effect as ifthey were ap-t pliedvto the fabric itself. Example 12, below, embodiesAthis method of treatment.

Examplev 12 A warp consisting of ECDE 150 1,/0 1Z fi-ber glass yarn wasslashed with a Warp sizing containing equal a similar warp sizingcontaining no potassium nitrate.

p Both warps were woven into style 841 easement type fabric (4.4 oz./sq.yd., warp and fill ESDE 150 1/0V lZ, fiber glass yarn). p

y The control fabric was passed at feet/minute through a 6 foot longheat-cleaning oven maintained atla temperature of 1230 F.

The fabric containing potassium nitrate in thewarp sizv.

ing was processed through the same heat-cleaning'v oven maintained at atemperature of 1190'l F. atl 172 feet/ minute.

The two fabrics were finished identically'` with an acrylic latexfinish.

. Table 7 is a comparison of the strength and whiteness. of these twofabrics.

TABLE 7 Mullen Burst Tensile Strenght, 3 Tensile Strength 4 Whiteness 1Strength, P.s.i.2 P.s.i. After Static Fold, P.s.i.

. Warp Fill Warp Fill Fabric with Potassium Nitrate in Warp Sizing .932260 118 108 115 102 Control Fabric 845 181 100 80 77 54 1 Photoelectrictristimulus data obtained with a Bausch and Lomb Optical Co. Spectronic20 Color Analyzer. Photoeleetric tristimulus data reduced to whitenessvalue according to National Bureau of Standards circular C-429, R.

using equation (19) where W=1 for a MgO standard and W=0 for blac S.Hunter (7/30/42) 2 Owens Corning Fiberglas Corp. Standard Methods ofTest for Fiberglas Decorative Fabrics, Technical Report No. 175. TestNo. DF-5l1, Owens Corning Fiberglas Corp., Textile Product DevelopmentLaboratory, Ashton, R.I.

3 Owens Corning Fiberglas Corp. Standard Methods of Test for FiberglasDecorative Fabrics, Technical Report No. 175. Test No. DF-509 also ASTMD579-49.

f Owens Corning Fiberglas Corp. Standard Methods of Test for FiberglasDecorative Fabrics, Technical Report No. 175. Test No; 13E-505. p

Example 13 Three specimens of the same fabric as described in Example 1were treated with an aqueous solution comprising 3% potassium nitrateand 1.25% sodium nitrate. The fabric was squeezed, dried andheat-cleaned at 1040 F. for five seconds. The finished fabrics werewhite and had tensile strengths of 216, 223 and 220 lbs/in. width,respectively. The strengths, thus obtained (97% of the greige strength)are much greater than could be expected for either the potassium orsodium cation applied independently under the same conditions.

From all of the data presented in the foregoing Examples, it appearsthat the identity of the cation portion of the oxidizing salt has a verydefinite effect on the tensile strength of the fabric. It appears thatas the ionic diameter of the cation of the pre-treatment salt increases,the strength of the fabric increases. Although the phenomenon is notcompletely understood, it is theorized that as the sizing is removed bythe heat treatment, the small quantities of alkali metal in the glassmigrate to the liber surface and are lost, resulting in loss of fiberstrength. When -a cation according to the invention is applied, however,there may occur, after removal of the sizing, an ion exchange wherebythe cation replaces the migrating alkali metals in the glass. As aresult strength loss is terminated or even reversed.

Simultaneously with the above effects, the nitrate, chlorate and otheroxidizing agent releases oxygen at the surface of the glass where itimmediately combines with the organic sizing materials and assists intheir rapid oxidation and removal. The two materials working together,cation and anion, effectively and quickly yield a heatcleaned fabric ofremarkably good strength.

Many industrial fabrics are commonly heat-cleaned by placing rolls offabric in a batch typeoven and slowly raising the Vtemperature ofSOO-700 F. The temperature ismaintained in the oven for a total of 48-80hours. The use of the pre-treatment in accordance with this inventionwill permita reduction in oven time and will providean improvement instrength when used in the batch oven process.

In continuous heat-cleaning processes, furnace temperatures aregenerally kept at a somewhat higher level, i.e. commonly from 1150l350F., and sometimes .up to about 1500 F. However, due to the extremelyfast desizing times permitted by the present invention, the duration ofexposure becomes critical and cannot be controlled very carefully aboveabout 1250 F. on presently available equipment. Moreover, at very hightemperatures, a greater percentage of time is consumed in heating up thefabric, and the fabric may not even reach the operating temperature ofthe oven before it has left the heating Zone. Consequently, althoughtemperatures above 1250 F. are contemplated herein, such temperaturesrepresent a practical upper limit.

On the other hand, very low temperatures may take an inordinately longtime to provide adequate de-sizing in a continuous heat-cleaningprocess. A temperature of about 600 F. represents a practical lowerlimit for most purposes. In any event, the temperature must besufficiently high to fuse the metal salt.

The actual selection of the precise time and temperature of operationwill be in large part dependent on the type of fabric being treated andits end use. Where strength is the primary consideration, such as in theindustrial eld, the time of exposure would be extended sufficiently togive maximum strength; further improvements may be achieved by operatingat lower temperatures. However, if cleanliness and speed are theoverriding considerations, one could select a high temperature and atime of exposure less than that required to `get maximum strength.

It is to be appreciated that the process of this invention can beapplied equally well to all types of fiber glass including yarns,rovings and the like. In accordance with the principles of the presentinvention, the strength of such forms of glass fabrics is substantiallyincreased.

Although the present invention is described above in terms of specificexamples and illustrative embodiments, it is to be appreciated that theprocesses disclosed may be altered by one skilled in the art without`departing from the spirit and scope of the invention.

What is claimed is:

1. The method of heat-cleaning a cation-containing fibrous glass toremove the sizing material on the surfaces thereof comprising the stepsof treating the glass with an oxidizing salt having a cation selectedfrom the group consisting of potassium, sodium, cesium and rubidium,said selected cation being at least as large in atomic radius as acation in said fibrous glass, and then introducing the glass, while dry,to an area wherein the glass is heated to a temperature of between about600 to l250 F. for a period of time at least sufficient to removesubstantially all ofthe sizing material and to yield a cleaned fibrousglass having a tensile strength of not less than about 60% of `that ofthe greige fibrous glass.

2.' The method according to claim 1 wherein the oxidizing salt isselected from the group consisting of nitrate and chlorate. Y t

3. The process according to claim 1 wherein the oxidizing-salt isapplied to the fibrous glass as a mixture with the sizing material.

4.k The method according to claim 1 wherein after heating the glass fora period of time sufficient t-o remove substantially all the sizing,rtheheating is continued at least until the tensile strength of said glassis increasing with time. f

5. method according to claim 1 wherein the glass 17 is heated for aperiod of time sutiicient to produce a whiteness thereon which in termsof luminous apparent reectance is at least 90% yas white as the greigefabric.

6. The method according to claim 1 wherein said fibrous glass is treatedwith said oxidizing salt by impregnating said brous glass with anaqueous solution of said salt, and thereafter drying said impregnatedbrous glass prior to the introduction thereof in the heating area.

7. The method according tol claim 1 wherein the glass is treated with amixture of oxidizing salts comprising two or more of said cations.

8. The method according to claim 7 wherein the glass is treated with amixture of sodium nitrate and potassium nitrate.

9. The method of heat-cleaning a cation containing fibrous glass toremove the sizing material on the surfaces thereof comprising the stepsof treating the glass with an oxidizing salt having a cation selectedfrom the group consisting of potassium, sodium, rubidium and cesium,said selected cation being at least as large in atomic radius as acation in said brous glass, and then introducing the glass, while dry,to an area wherein the glass is heated to a temperature suicient to fusethe xidizing salt and to burn oli said sizing material, said temperaturebeing maintained for a period of time at least References Cited UNITEDSTATES PATENTS 2,674,549 4/1954 Balz 134-2 2,779,136 l/1957 Hood et al.3,232,788 2/1966 Morzocchi et al.

OTHER REFERENCES Stresses in Glass Produced by Nonuniform Exchange ofMonovalent Ions, pages 59-68 of the Journal of Pm. Ceramic Society, vol.45, No. 2, by S. S. Kistler. Measurement of the Mechanical Strength ofGlass After Reinforcement, by Acloque and J. Tochon.

U.S.C.V. Symposium sur la Resistance Mechanique du Verre et les Moynesde lameliorer (1961), pp. 687-704.

DONALL H. SYLVESTER, Primary Examiner. R. L. LINDSAY, AssistantExaminer.

UNITED STATES PATENT oFFIcE CERTIFICATE OF CORRECTION Patent No. 3 ,375`,1SS` March 26 1968 Richard G. Adams It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 3, line 25, "gabric" shou1d read fabric line Z9, before "strong"insert as Column 4, line 52, "valve" should read value Column 6, line43, "considerating" should read considering Column 8, line 73,"reepated" should read repeated Columns 11 and 12, TABLE 5, tenthcolumn, line 12 thereof, "'4.5 Hrs." should read 4 5 Min. same column,1ine 13 "6 .5 Hrs should read 6.5 Mn. TABLE 6 tenth column, line 5thereof, "20 Min. should read 2O Sec. same TABLE 6 tenth column, line 6thereof, "30 in." should read 30 Sec. Column 13, line 6, "speciment"should read specimen line 54, "weight" should read wet Column 14, line46, "wih" should read with line 63 "ESDE" should read-H ECDE`'. Columns15and 16, TABLE 7: third and fourth columns, in the heading, line 1thereof "Strenght, 3" should read Strength,3 Column 18 ILine 13,"Morzocchi" should read Marzocchi line 17 ','Pm Shou1d read Am.

Signed and sealed this 23rd day of September 1969.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

